The Woman in Cabin 10 is a 2016 mystery novel by Ruth Ware. The book opens with main character, Lo, experiencing a burglary in her basement flat in London. She is trapped inside her bedroom and has to fight her way out; after the event, she experiences severe insomnia and symptoms of post-traumatic stress that alter her view of her own safety and strength.

After the burglary, Lo lashes out at her boyfriend, Judah, who is frequently out of town and wasn't there to help her cope. Lo departs for a cruise on a luxury boat called the Aurora Borealis, which she is covering as part of her job as a travel journalist while her boss in on maternity leave. The boat is owned by Lord Richard Bullmer, a London business tycoon, and his wife, heiress Anne Bullmer.

At first Lo struggles to enjoy her trip due to her paranoia from the burglary. Then, her first night, she wakes to the sound of a woman's scream, and the sound of a splash. She is certain that she has just heard a body being dumped into the North Sea. When she investigates, she sees a smear of blood on the glass veranda door leading into the room next to her own.

Nobody believes Lo's testimony about the woman next door, whom Lo believes is the victim of the murder. Despite Lo visiting the room the night before, to borrow mascara, the cabin is now empty, and according to ship records, it was never occupied by any guest. Lo continues to investigate the murder, despite the doubts of head of security Johann Nilsson and many of the ships high-powered guests. However, the more she investigates, the more dangerous the situation becomes. Lo is threatened by an anonymous guest, and begins to feel more and more insane.

The situation comes to a head when the woman from the cabin next door appears, miraculously alive. She lures Lo to the ship's lower decks and then traps her in a cell far below the water line, near the engine. Lo discovers that the woman is working with Richard Bullmer, and that she is a mistress impersonating Bullmer's wife, Anne, who is dying of cancer. Carrie, the mistress, reveals that Bullmer snuck her aboard and then convinced her to help him remove the dead body of his wife from the ship, after she died in what Bullmer claims was an accident caused by a domestic dispute.

Lo becomes more frantic to escape and bonds with Carrie enough to convince Carrie to set her free. She escapes into the Norwegian fjords and after a run-in with a corrupt hotel manager and a similarly corrupt police officer, Lo is finally rescued by a gentle, elderly Norwegian farmer, who takes her to the police station where she can report her story.

Ware reveals that two bodies have been dredged from the North Sea: the body of Richard Bullmer, who appears to have died by suicide; and the body of a young woman with a shaved head that Lo believes is Carrie. Lo is devastated, but continues on with her life, agreeing to move to New York with her beloved partner, Judah.

In the last sections of the novel, Lo is surprised to discover that the female body found in the sea belongs to Anne Bullmer, and that Richard Bullmer's gunshot wound was not self-inflicted after all. Later, Lo is wired money from a mysterious bank account based in Switzerland, which Lo believes must belong to Carrie.